The invention relates to an apparatus for damping courses of movement (semi-active damping). In a known apparatus of this type (U.S. Pat. No. 3,807,678), in a suspension system having two masses, one of which may be one or more wheels of a vehicle and the other of which may be the vehicle body, a passive standard compression spring is disposed between the two masses and is called a passive separating member, with a so-called active damper connected parallel to it. This damper, in which a piston slides in a cylinder, dividing it into two work chambers, is considered an active damper because there is an active intervention, as it were, into the damping properties, or in other words the positive volumetric displacements of the pressure fluid in the respective working halves of the damper by control means. To this end, the two work chambers are connected crosswise and parallel to one another via valves pointing in opposite directions and allowing a flow of the pressure fluid in only one direction; the quantity of pressure fluid then allowed by these valves to pass through is "actively" determined by triggering of the of the valves accordingly by means of suitably prepared sensor signals. Since in this known suspension system the spring itself is completely passive but the damper is conceived of as active in terms of its properties, the overall system in this patent is called semi-active. This term is not logical in the context of the dampers of the present invention, however, which without referring to suspension systems not taken into account can themselves be called semi-active dampers and are therefore so called, for reasons that will be explained in further detail hereinafter.
It is also known to provide so-called active damping means in vehicle wheel suspension systems, see the article, "Active Damping in Road Vehicle Suspension Systems:, published in the journal Vehicle System Dynamics 12 (1983), pp. 291-316. This article is also cited because it describes fundamental concepts, in theoretically detailed form, especially for active damping properties.